A simple CO2 exchange model simulates the seasonal leaf area development of peatland sedges

Abstract

Sedges (Cyperaceae) are dominant plants in many northern wetlands and contribute to the carbon cycling in several ways. In order to more accurately estimate the carbon balance of a wetland it is essential to be able to simulate the temporal changes of the leaf area of the sedges. Our aim was to test the ability of a simple carbon dioxide (CO2) exchange model to predict the seasonal development of sedge leaf area index (LAI). The model simulates the development of sedge LAI that depends on carbon gain/loss in net photosynthesis, utilization of stored carbon in spring, and LAI decline due to senescence in late summer. The net photosynthesis model is driven by LA!, air temperature, water table depth and photosynthetically active radiation. We parameterized and validated the model with two years of observational LAI data from two boreal pristine peatland sites and included data points from both pristine and manipulated (drainage and warming) treatment plots. Model parameter values other than the timing of the start of senescence, LAI decline rate in senescence and size of carbon storage were independent of observational data. The model successfully simulated the seasonal course of LAI development and is thus an easy and adjustable tool for producing estimates of sedge LAI for other peatland sites. It can be adjusted to different sites although it cannot predict the exact LAI level of a site that is controlled by site characteristics. Its ability to simulate the interannual variation in this two-year dataset was inadequate so there is a need to test the model against longer time series of measured LAIs in order to validate models' capability to predict the interannual variability of LAI.